Communications system of restricted-range type



Sept. 11, 1951 w. s. HALSTEAD Filed May 5, 1947 MULTI- CHANNELCOMMUNICATIONS SYSTEM OF RESTRICTED RANGE TYPE 5 Sheets-Sheet 1 l I JWILLIAM S. HALSTEAD INVENTOR Sept. 11, 1951 w. s. HALSTEAD 2,567,431

comumcmons SYSTEM OF RESTRICTED RANGE TYPE Filed May 5, 1947 5Sheets-Sheet 2 WlLLIAM S. HALSTEAD INVENTOR ATTORNEY In!" llllll I IlSept. 11, 1951 w. s. HALSTEAD 2,567,431

COMMUNICATIONS SYSTEM OF RESTRICTED RANGE TYPE Filed May 5,1947 5Sheets-Sheet 5 FIG. 5

, WILLIAM S. HALSTEAD INVENTOR BYW ATTORNEY Sept. 11, 1951 w. s.HALSTEAD COMMUNICATIONS SYSTEM OF RESTRICTED RANGE TYPE Filed May 5,1947 5 Sheets-Sheet 4 FlG. ll

WILLIAM S. HALSTEAD INVENTOR BY J ATTORNEY Sept. 11, 1951 W. S. HALSTEADCOMMUNICATIONS SYSTEM OF RESTRICTED RANGE TYPE Filed May 5, 1947 5Sheet-Sheet NQJ v v v FCC 8 H H 8 u. T 6 mm 81 2 m mm #9 N mm 0 x? M9N0- i ww fi QE 8 WILLIAM S. HALSTEAD INVENTOR ATTORNEY Patented Sept.11, 1951 COMMUNICATIONS SYSTEM OF RESTRICTED-RANGE TYPE William, S.Halstead, Purchase, N. Y.

Application May 5, 1947, Serial No. 745,926

10 Claims.

This invention pertains to restricted-range induction-radiocommunications systems and apparatus therefor, and more particularly toa system for providing individualized reception of induction radiosignals within a specific seating area encompassed by a horizontaltransmitting loop on which one or more radio carrier frequencies,modulated by audio-frequency signal energy, have been impressed.

The invention is related to the general subject matter ofrestricted-range radio communications as disclosed in my co-pendingapplications, now abandoned, for United States Letters Patent, SerialNumbers 570,051 for Induction Radio System and 570,052 for Radio SoundDistribution System, and the disclosures of this application areconsidered to be improvements thereon.

Heretofore it has been customary to utilize electronic speechamplification equipment with associated loudspeakers or headphones indistributing to listeners within the seating area of a hall, auditoriumor theatre the sounds associated with the voice of a speaker, music, orother intelligence addressed to the occupants of the seating area. Insome instances, as in providing for persons with deficient hearing, orin conveying several language translations oi a speakers voice atinternational conferences. radio carrier signals, modulated by audiofrequencies derived from speech amplification equipment and associatedmicrophones or sound records, have been impressed on a horizontaltransmitting loop encompassing the seating area by means of a carriertransmitter. Through the use of portable re ceivers and associatedheadphones, listeners within the seating area have been able to hear thesounds as transmitted by the system. An arrangement of this general typeis shown in my co-pending applications, Serial Nos. 570,051 and 570,052.In applications of the system in which several difierent languagetranslations of a speech are transmitted concurrently within the seatingarea, different carrier frequencies are employed for the variouslanguage translations, as is also described in my co-pendingapplications, Se-

rial Numbers 570,051 and 570,052. The listener While receivers of thisgeneral type have been successfully employed in practice, as at severalconferences oi the United Nations, a problem has presented itself withrespect to the distribution and utilization of the portable receivers,particularly in large seating areas in which several thousand personsmay desire to use the individual receiving equipment. It is apparentthat at a large gathering of this size, a major problem would beinvolved in providing each person with a receiver, in collecting thereceivers after the event, and in preventing theft of the receivers. Inaddition, if the receivers utilize vacuum tubes and batteries, a seriousproblem is presented in that each receiver must be checked prior to itsuse to determine that the tubes and batteries are in proper operativecondition, and must again be checked after each period of use toascertain that the battery switch in each receiver has been thrown tothe off position by the person who has employed the unit.

A further problem has presented itself in connection with the operationof group-address system of the radio-carrier type in that interceptionof the signals at points outside of an auditorium area in which aconference is held may be accomplished by anyone possessing a radioreceiver tuned to frequencies employed by the transmitting system. Insome instances, this may be highly undesirable, especially in certaininternational conferences where a degree of security is to bemaintained.

These and other considerations have resulted in the invention of thepresent application. In the system of the invention, each receiveremployed by a listener in the seating area becomes a part of the chairutilized by him. A loop antenna, which is an integrated portion of thechair receiver structure, is mounted in a position for optimum signalpick-up beneath the seat of the chair, with the volume control andtuning switch located on a tuning head disposed at the side of the seatin a position convenient for the user. Adjustable elastic straps areemployed to hold the receiver in position on the chair, therebyfacilitating the attachment and removal of the chair receiver withoutthe use of tools or mounting fixtures capable of defacing or in any waydamaging the finish of the chair.

Inasmuch as the receiving means may be quickly and easily attached toany conventional type of chair, the system may be installed withoutdifflculty in the average auditorium, theatre or other places ofassembly equipped with chairs of various types. Also, as the chairreceiver can readily be affixed in position by authorized personnelprior to an event, such as an international conference, and may be leftin position on the chair for a series of conferences, it may be seenthat no problem of receiver distribution to each listener is presented.Since the reeeiver is not removable by the listener after each period ofuse, and is in such form that it could not be readily be stolen withoutdetection by others in the seating area, a solution to the problems ofdisposal of the receiver after each event and its possible theft hasbeen found.

While a preferred form of chair receiver of the present invention is ofa non-vacuum tube type, and requires no batteries, it is possible thatfor some applications of the system, receivers of vacuum-tube type ofrelatively high sensitivity may be desired. Therefore, to assure thatbattery power is removed from vacuum tubes at the end of each period ofuse, means are disclosed to enable the automatic disconnection ofelectric power in chair receivers of the vacuum-tube type when thelistener rises from his seat at the conclusion of an event. Thus, at theend of a days session at an international conference, for example, thebatteries of the chair receiver are automatically disconnected from thevacuum tube circuits, thereby preventing the accidental discharge of thebatteries through failure of the listener to turn the power switch tothe off position.

Means are also disclosed whereby an antiinterception, or jammingtransmitter, operating on the same or substantially the same carrierfrequencies employed by the group-address transmitter, is so arranged asto preclude reception of an intelligible signal from the group-addresstransmitter at points outside of the seating area served by it, withoutcausing interference with the group-address signals at points within theseating area.

It is one of the objects of this invention to provide a restricted-rangeinduction-radio communications system and apparatus therefor wherein asignal-emanating means is disposed adjacent a seating area provided witha radio receiver individual to each of the seats therein, and with meansfor connecting from a central transmitting station to the radioreceivers over a plurality of radio-frequency signaling channels ofdiflerent carrier frequencies.

A further object of the invention is to provide a system employing amulti-channel transmitting station connected to a signal emanating meanswhich is disposed to concentrate the transmitted signal in a localizedseating area wherein one or more radio receivers are located in eachchair structure and adapted for selecting the desired frequency from themulti-channel transmitter as desired by the listener at each chair.

A further object of the invention is to provide a transmitting systemutilizing a multi-channel transmitter having its output connected to asignal emanating means for concentrating the transmitted signal in aspecific area and having a multiplicity of modulated carrier wavetransmitters, each connectable for modulatin one carrier frequency ofthe multi-channel transmitter, and at least one radio receiver of chairtype responsive to the carrier signals emitted by the multi-channeltransmitter, disposed in the area of the concentrated transmittedsignal, with the receiver having a switching means for selecting theparticular channel desired to be utilized by the operator of the radioreceiver.

, tor of a radio receiver disposed within a chair structure in theseating area.

A further object of the invention is to provide a restricted-rangeinduction-radio communications system utilizing a multi-channelfrequency transmitter having its output connected to a loop-type signalemanating means disposed abouta seating area wherein a speakers voicemay modulate one channel of the transmitter, said speakers voice to bereceived by a multiplicity of radio receivers for the benefit oftranslators so that the translators may translate the received messageof the speaker, and thereafter each of said translators may speak into amicrophone, individual to each translator, for modulating a separateradio frequency channel of the multi-channel transmitter to the end thatan occupant of a seat within the confines of the signal emanating meansmay select the signaling channel of the particular translator desired.

A further object of the invention is to provide a simplified form ofradio receiver for use in conjunction with the system set forth hereinwherein the receiver may have as an integral part thereof a horizontalloop-supporting housing, with a loop disposed therein, and means securedto the loop-supporting housing for disposing and securing the loopbeneath the seat of a chair in a position for effective reception ofradio-carrier signal energy from a horizontal transmitting loop disposedabout the seating area in which the chair is located.

A further object of the invention is to provide a loop-structuresupporting member with a loop-structure housing angularly disposablethereto for positioning the radio receiver loop to obtain maximum signalstrength from the signal-emanating means of the system.

A further object of the invention is to provide a radio receiver havinga loop-structure housing disposable below the seat of a chair andpositionable in relation to the seat of the chair in such manner as toreduce the effect of body capacity resulting from proximity between theoccupant of the chair and the loop, and in such manner as to providemaximum signal reception from the signal-emanating means of thetransmitting system.

A further object of the invention is to provide a radio receiver havinga loop-structure housing with means secured to the loop-structurehousing for positioning and securing same to the area beneath the seatof a chair or the like.

A further object of the invention is to provide a flexibleloop-structure housing having a metallic conductor as a part thereofwith said loop structure housing having resilient fastening means formounting same on the seat of a chair or the like, with the structurehousing having as an integral part thereof, a radio receiver disposed atthe side of the seat of the chair and within easy reach of the occupantthereof.

It is an additional object to provide a receiver, mountable on a chair,wherein electric power for Operation of vacuum tubes within the receiveris CROSS HlzHiRENCE ber of vacuum tubes to amplify and rectify aninduction-radio carrier wave of specific radio carrier frequency.

It is a futher object to provide an induction radio signaling systemwherein interception of intelligence addressed primarily to occupants ofa designated seating area is precluded at points substantially outsidethe seating area.

Further and other objects may become ap parent from a perusal of thedisclosure herein, and it is to be understood that modifications andchanges may be made without departing from the spirit of the subjoinedclaims.

In the drawings:

Fig. 1 is a combination pictorial representation of the system inconjunction with a partial schematic wiring diagram thereof andparticularly of one preferred form of induction radio receiver of anon-vacuum tube type.

Fig. 2 is a partial front elevational view of a representative chairwith a radio receiver and loop-structure housing connected thereto.

Fig. 3 is a plan view of the loop-structure housing and integral radioreceiver having means for securing and positioning same to a chair, withtuning controls at the side of the seat thereof.

Fig. 4 is a front view of a loop structure housing as set forth in Fig.3.

Fig. 5 is a modification of the loop-structure housing and securingmeansfor disposing and securing said housing below the seat of the chair andspaced therefrom, with means for positioning the loop housing formaximum signal reception in relation to the horizontal transmittingloop.

Fig. 6 is a plan view taken along lines 6-6 of Fig. 5 showing a portionof the loop-structure housing supporting and securing means, with theradio receiver or tuning head disposed on one side thereof, to be easilyreached by the occupant of the chair.

Fig. 7 is a side view of the loop-structure housing shown in Fig. 6,said loop-structure housing being angularly disposable in a verticalplane by an adjustable loop-structure supporting member which carriesthe radio receiver and the means for securing the loop-structuresupporting member to the chair.

Fig. 8 is a plan view of Fig. 7, more clearly showing the loop-structuresupporting member having the radio receiver secured thereto, and

I also having thereon the means for securing the loop structuresupporting member to the chair and for positioning the loop-structurehousing in relation to the loop-structure supporting member.

Fig. 9 is a partial perspective view of a chair showing theloop-structure housing angularly disposed in relation to the loopstructure supporting member which is substantially parallel with thehorizontal portion of the chair seat.

Fig. 10 is a perspective view of a modification of the loop-structurehousing wherein said housing is a part of a flexible cover for the chairseat and fits on the upper surface of said chair seat, with securingmeans for holding the loop-structure housing in position on the seat ofa chair, with the tuning head disposed at one side of the housing.

Fig. 11 is a plan view of the flexible loop- -structure housing shown inFig. 10, said loopstructure housing having cut-away portions for fittingon the particular chair to be used. with the radio receiver secured tothe flexible loop-structure housing at one side thereof.

Fig. 12 is a schematic wiring diagram of one preferred form of inductionradio receiver employing a vacuum tube and a crystal to attain greatersensitivity than is provided by the nonvacuum tube receiver of Figure 1.

Referring to the drawings and more particularly to Fig. 1, there isshown schematically an auditorium area l6, having a signal emanatingmeans I 6 in the form of a horizontal loop disposed within theauditorium area and embracing a seating area, consisting of seats ll,having an induction radio receiver I8, and a horizontal loop I9 (showndotted) connected to the radio receiver on each of the seats. Aheadphone unit, such as 42, is associated with each chair receiver. Amulti-channel radio carrier transmitter 20, or equivalent group ofsingle-channel transmitters, has its output connected to terminals 2|and 22, which terminals are connected to the ends of the signalemanating means, such as transmitting loop l6. A master microphone 23 isconnnected to the multi-channel transmitter 26, and secondarymicrophones, such as 24 and 24' are located in individual soundproofbooths 25 and 25', as shown, each of said microphones 24 and 24' beingconnected to their respective input circuits of multi-channeltransmitter 20. An induction radio receiver 26, termed a secondaryreceiver since it is associated with a secondary microphone, such as 24,is located in each of the soundproof booths. While the secondaryreceivers, such as 26, are shown outside of the signal emanating meansl6, it is to be understood that the signal emanating means may bedisposed to embrace the area wherein the secondary receivers are locatedin the soundproof booths 25, and that the secondary receivers 26 arewithin the effective signaling range of the signals impressed upon thesignal emanating means, or transmitting loop l6.

Conductors 21 represent conventional electriclight and power wiringwithin the building, of which the auditorium area 15 is a part. It is tobe understood that the conductors 21 may be any conventional electriclight or power wiring which would ordinarily be used in an auditorium,theatre, general assembly room or the like, and need not be speciallyinstalled for application with the present invention. Ananti-interception transmitter 28 is shown having its output connected toR. F. transmission line conductors 29 and 30, which are connected to oneside of condensers 3| and 32, the other side of said condensers beingconnected to the terminals 33 and 34, which are connected to theconductors 21.

Junctions 35 and 35', and conductors 36 and 36', respectively, areemployed to connect the input circuits of multi-channel transmitter 20and the input circuits of the anti-interception transmitter 28 toconductors 29 and 39', respectively, which are connected with thesecondary microphones 24 and 24', respectively.

The anti-interception transmitter may transmit a group of carrier-wavefrequencies substantially the same as those of multi-channel transmitter20, or a carrier wave having a varying frequency which sweeps throughall the frequencies used by multi-channel transmitter 20. Theseantiinterception frequencies are impressed upon the conductors 21through R. F. coupling condensers 3| and 32, and will mutilate thesignals from trans- EXAMINEF mltter 2| at receiving points outside ofthe conference room area I5, as will be described in further detail insubsequent paragraphs. The master microphone Z3 and the secondarymicrophones, such as 24 and 24', will each be used to modulate onechannel of the multi-channel transmitter 20 and simultaneously modulateall channels of the anti-interception transmitter 28.

The operation of the multi-channel transmitter 20 is such that a speakerusing the microphone 23 will cause his voice to modulate a designatedchannel of the transmitter 20 or selected group of channels oftransmitter 20 whose output circuit connected to the transmitting loopIS. The chair receivers, such as l8 and I8, located within the confinesoi the transmitting loop l6, and the secondary receivers 26 and 25 whichmay also be located within the range of the induction field of transmittng loop IE, will be able to receive, with maximum eiiectiveness, signalsimpressed upon the transmittin loop by the multi-channel transmitter 20,thus enabling the speaker to have his voice carried to listeners in thegeneral seating area who employ the radio receivers, such as l8 and I8.One or more persons, in an illustrative application of the system of theinvention, may act as a translator and be located in each of the booths,such as 25 and 25'. The translators may listen through the headphones 40and 40 of the secondary receivers 26 and 26, respectively, and hear thevoice of the speaker which is impressed upon the master microphone 23.Assuming that the person using the master microphone 23 is speaking inFrench, the translator located in the booth 25, for example, will hearthe speech of the speaker in his headphone 40. The translator may thentranslate the language of the speaker at the master microphone intoanother tongue, for instance English and, utilizing the Englishlanguage, speak into the secondary microphone 24. His voice willmodulate one of the channels in the multi-channel 20 and also modulateall channels of the anti-interception transmitter 28. The translators ineach of the other booths, such as 25, may use the same procedure as thefirst translator, but may speak into their respective secondarymicrophones, such as 24, in difierent languages, for instance, inChinese, Russian and Spanish. Their voices will then each modulate onechannel of the multi-channel transmitter and all channels of theanti-interception transmitter 28.

It will therefore be seen that while the speaker at the mastermicrophone 23 may have his voice heard by means of individual radioreceivers, such as I8 and I8, it will also be possible for the listenerat the radio receiver l8, for example, to receive the voice of any ofthe translators by utilizing a channel selector switch 41, in theillustrative receiver l8. The arm of selector switch 4|, in theillustrative example, is of rotary step type and may be connected to anyof the contacts, such as 43, 44, 45, 45 or 41, each of which has apre-set adjustable trimmin condenser, such as 48, $5, 50, 5! and 52,connected respectively therewith. The receiver loop I9 is connected toone side of loop tuning condenser 54 and ground terminal 53 of thereceiver l8, with a tap 55, at a position several turns from the lowerend of the loop, to connect the first several turns of the loop to oneside of the crystal diode detector 56 in eflecting a proper impedancematch and improved selectivity. The headphones 42 are connected betweenthe other side of the crystal diode detector 55 and the ground terminal53, to which the arm of switch 4| is connected. An R. F. by-

pass condenser 51 is shunted across the headphones 42 in conventionalmanner. By movement of the arm of selector switch 4| to any of theterminals 43 through 4?, any receiving channel may be activated by theinsertion of the proper tuning condensers 48 through 52. Whileadjustable trimming condensers are specifically shown in the circuit forresonating the loop circuit at each of the specific transmittingchannels, it is to be understood that any suitable tuning circuit may beused in lieu of that shown in Fig. 1

The electromagnetic field 5B surrounding the conductors of loop I6 isutilized in transferring signal energy between the transmitting loop 15and the receiver loop l9. While much of the signal energy from themulti-channel transmitter 20 is concentrated within the confines of thetransmitting loop l6, it will be apparent that signals will emanate fromthe transmitting loop outside of said loop, and consequently, outside ofthe auditorium. To reduce the posibility of interception of intelligibleradio signals beyond the confines of the auditorium, all channels of theanti-interception transmitter 28 are modulated simultaneously by thevoices of the several translators using the microphones 24, A receiver31 located on the outside of the auditorium, as shown in the diagram ofFig. 1, will, by virtue of its greater proximity to electric power lines21 than to the transmittin loop l6 and because of the partial shieldingeffect of the wall of the auditorium area I5, respond principally to the"Jamming signals from the anti-interception transmitter, operating onthe same carrier frequencies employed by the transmitter 20.Consequently, the relatively weak signal emanating from the transmittingloop I6 beyond the confines of the auditorium will be dominated by thestronger signal impressed upon the outside power lines, such as 21 andwill be so mutilated by the simultaneous presence of all the voices oithe translators as to be unintelligible.

A receiver, such as I8, disposed within the auditorium area 5 and havinga horizontal loop antenna 19 will be responsive, in an efiective manner,only to the intense concentrated electromagnetic field produced withinloop I5, and will not respond in an efiective manner to the relativelyweak interfering signal produced by the anti-interception transmitter 28and its associated power line conductors 21 on the outside of theauditorium area. Further discrimination between the desired signals fromtransmitting loop I8 and those from power line conductors 21 is providedby the horizontal disposition of the receivin loop 19. The horizontalloop IE will provide a maximum signal from carrier energy impressed onhorizontal transmitting loop l6 and a minimum signal from carrier energyimpressed on power lines 21. That is, with a given loop receivingantenna, such as IS, the strongest signal will be received fromhorizontal transmitting loop H5, at a point within the loop. when thereceiving loop 19 is disposed in a horizontal plane. The same receivingloop is will provide the strongest signal from carrier energy impressedon power-line conductors 21 when the receiving loop 19 is disposed inthe vicinity of power conductors 21 and in a vertical plane. Thus, byvirtue of the considerable differential which exists between theintensity of signaling fields produced respectively by the horizontaltransmitting loop [6 and the power lines 21, and by virtue of thehorizontal disposition of the receivin loop l9, which is responsive inan optimum manner to the signaling field produced by horizontaltransmitting loop Is, a great degree of discrimination is producedbetween the .two signals at pointswithin the transmitting loop. On theoutside of transmitting 100p I6, however, it has been observed that aloop receiving antenna must be inclined at an angle with respect to thehorizontal plane of .the transmitting 100p l6. and as the distance.increases between the receiving loop and transmitting loop It, theangular disposition of the receiving loop approaches a vertical plane.Thus, on the outside of the seating area I5, the degree of planardiscrimination, which is an important factor when the receiver is withintransmitting loop It, becomes relatively insignificant, therebyrendering it more diflicult to intercept intelligible signals at pointsexternal to the seating area.

While one form of signal mutilation is presented herein, it is to beunderstood that any other conventional form of signal mutilation orjamming may be employed.

Referring to Fig. 2, a front elevational viewof a chair 59 illustratethat a loop-structure housing 60, with flexible straps, such as 6|,secured thereto, is mounted in a horizontal position beneath the seat59A of the chair 59. A radio receiver, termed a tuning head 18, issecured to the loop structure housing and is held at the side of theseat 59A, with tuning control 66 in a vertically-disposed positionaccessible to the occupant of the chair.

Fig. 3 shows a top view of the loop-structure housing 60, having themetallic loop Is as a part thereof. The metallic loo may be disposed onone surface of the loop structure housing or may be disposed between twolayers or sheets of suitable non-conducting material. The flexiblestraps GI have buckles 65 or other fastening means of any well-knowntype on one end thereof, with the other end thereof being secured to theloop-structure housing. Flexible straps 62, in the illustrativearrangement, have perforations therein and are used to engage thebuckles 65 of the straps 6| for positioning and securing theloop-structure housing on the legs of the chair below the seat, as shownin Fig. 2. The tuning head I8 is attached to loopstructure housing 60 atone side thereof, and includes channel selector control knob 66 andvolume control knob 61. A headphone 42 is connected to the tuning headIt by means of cord 68.

Fig. 4 shows, in side view, the loop-structure housing 60 with tuninghead l8 as a unitary member and, as shown in Fig. 3, the loop is a partthereof. It will be seen from Figs. 2 and 3 that the control knobs 66and 61, when the radio receiver is in position on a chair for use .bythe occupant of the chair, may be easily reached by the right hand ofthe chair occupant. It will be observed by reference to the variousviews of the chair receiver, as shown in Figures 2-4, that by utilizingthe straps GI and 62, it .will be seen that the loop-structure housing60 with its associated tuning head I8 may be placed beneath the seat ofa chair and may be positioned any distance below the seat by adjusting.the straps at the proper height on the legs, from the floor.

; Fig. shows a chair 1! having a seat portion I2. Aioop structurehousing 60, similar to that of Figs. 3 and 4, has straps 16 and 16connected ture housing and the other end attached to a flatloop-structure supporting member 15. Thus the two straps 16 and 16', inaddition to straps 11, Fig. '1, hold the loop-structure housingsuspended beneath the loop supporting member 15. The loop supportingmember has elastic straps, such as 10 and 13 which are adapted to goacross the top of the seat 12 of chair 1| and may be connected to theopposing sides of the loop supporting member 15. The tuning head l8,similar to that of Figs. 2-4, is shown with the control knobs, such as51, at the left side of the chair, as observed by the occupant, with theheadphones 42 connected by a cord 68, to the tuning head.

Fig. 6 is a top view of the seat 12 illustrated in Fig. 5, showing thetuning head 18 and straps 10 and 13 positioned for use on the chair 1 I.The straps 13 and 10 are shown disposed across the upper surface of theseat 12, to hold the tuning head I8 and its complemental loop members,such as 15 and 50, Fig. 5, in position for use on the chair. Theheadphones and headphone cord, 42 and 68 respectively are shownconnected to the tuning head l8. A pressure-actuated battery switch I00of any well-known fiat type may be disposed in strap 13, as indicated bydotted lines, to operate with a modified form of chair receiver in whichone or more vacuum tubes may be used,

as will be described hereinafter. It is obvious that disposition of thepressure switch in this manner on strap 13 may cause the switch to closewhen a person occupies the chair. and to open when he rises from thechair, thus automatically disconnecting battery power from the vacuumtube or tubes which may be utilized, in some instances, in the chairreceiver.

Fig. '1 shows in side elevation the loop-structure supporting member 15with a portion of the strap 13 being secured thereto. The straps 16' and11 are shown having one end secured to the loopstructure support 15,with the other ends thereof being secured to the loop structure housing60. The straps 16' or 11 may be adjusted in length, as shown by thedotted lines in order that the loopstructure housing 60 may be movedangularly in a vertical plane with respect to the horizontal position ofthe loop-structure support 15 for increasing the dielectric spacebetween the loop and metallic elements which may be in the seat 12, orto minimize the effect of body capacity which in some instances mayexist between the body of the occupant of the chair and the loop per se;proper angular disposition of the loop-structure housing '60 alsois'important to effect maximum signal pickup by the loop when located atcertain points within the auditorium area where the normal horizontaldisposition of the loop does not produce the optimum signal strength atthe receiver.

Fig. 8 illustrates in further detail the general arrangement of thechair receiver of Fig. '7 and shows the loop-structure support 15 havingthe tuning head I 8 secured thereto, with the loopstructure housing 60suspended from the loop structure support 15 by the straps, such as 16,16 and 11. A snap fastener 63, of any well-known type is disposed at oneend of strap 13, and a coacting fastener means 63A is shown onloopsupporting member 15 to permit ease of installation or removal ofthe chair receiver from seat 12.

Fig. 9 shows a perspective view of the chair receiver and itscomplemental parts positioned for use on the chair by the occupantthereof. The loop structure housing 60 is shown angularly disposedbeneath the seat 12 of the chair 1 I, in much thereto, with one endattached to the loop-struc- 76 the same manner as the loop-structurehousing ii is inclined as shown by the dotted lines 80" in Fig. 7.

Figs. 10 and 11 show modifications of a flexible loop-structure housing18, in slip-cover form, which has cut-away corners 19 to better adaptthe medium to fit over the seat of the chair. The tuning head I8 issecured to one edge of loopsupporting structure I8 and forms a partthereof. In Fig. 11. the flexible loop-structure housing 18 is shown inextended plan view before it is secured to the chair seat. Straps I and80 each have one end thereof secured at corners of the flexibleloop-structure housing, and snapfastening members 8I and 82 are securedto the straps I9 and 80, respectively, and are used for sitioning andsecuring the flexible loop-structure housing I8 as a seat cover on thechair II. When the flexible loop-structure housing is secured to thechair, the area indicated by 83 is folded as shown in Figs. 10 and 11 toform a tight fitting cover on the upper surface of the chair seat, withthe folds I08 and I 09 forming a dividing line between the horizontaland vertical sections of the cover.

While straps with buckles or snap-fasteners are shown in several of theviews for positioning the loop-structure housing to the loop structuresupport, it is to be understood that any other method or means ofindicating or positioning the several members in relation to one anothermay be utilized.

One preferred form of illustrative induction radio receiver,incorporating a vacuum tube radio frequency amplifier and crystal diodedetector, suitable for use with the system described herein, is shown inFigure 12. In this receiver circuit. one terminal of loop antenna 85,which may be wound on a fibre board or other suitable form to be mountedbeneath the seat of a chair, as shown in Figs. 2 and 3, is connected asshown to the control grid of vacuum tube 85, employed as a tunedradio-frequency amplifier. The other terminal of the loop 05 isconnected through condenser 81, to ground and to one side of automaticvolume-control resistor 88, utilized in automatic volume controlfunctions as will be described hereinafter. Tuning of the loop circuitis accom plished by means of selector switch 89 and associatedcapacitors such as 50 and III. In the illustrative arrangement, amulti-position rotary switch is utilized together with five adjustablecondensers, such as 90 and SI, to effect tuning of the loop circuit toany one of five predesignated carrier frequencies, employed by theillustrative communication system described herein. Tuning of the outputcircuit of vacuum tube 86 is accomplished by means of avariable-permeability inductor 92 and associated capacitor selectionswitch I08, the arm of which is joined with the arm of switch 89 bymeans of a common shaft 83, to which a tuning, or channel selector knob04 is afllxed. Preset adjustable condensers, such as 85 and 96 areutilized in connection with switch I08, to effect tuning of the outputcircuit of R. F. amplifier tube at to the desired carrier frequency,in'step with the'tuning of the loop circuit without individualadjustment of each tuning switch. Plate-supply by-pass condenser 9'! isconnected between the positive'side of the plate battery and ground asshown. A manually-operated switch 98 is employed to disconnect battery99 from the filament of vacuum tube 86 when the set is not in use. Asecond switch I00, of pressure-actuated type and of substantially flatconstruction, in series with manually-controlled switch as may beutilized as a part of the chair receiver structure, as explained inpreceding paragraphs, to automatically disconnect the filament from thebattery 99 when the seat is not occupied. This prevents accidentaldischarge of the battery 89 during periods when the seat is not occupiedand when a former occupant might have neglected to open switch 98 uponleaving the chair.

It is pointed out in this connection that an automatic body-actuatedswitch of the type described herein is of practical importance since itis assumed that large numbers of chair receivers will be utilized inauditoriums, convention rooms, theatres, and the like, which wouldotherwise present a problem of conservation of battery life were notsome automatic means provided to disconnect the battery from thefilament of vacuum tube 86, when the equipment is not in use. It is alsopointed out'that the disconnection of the filament battery 59, fromvacuum tube 06, also eiiects suspension of current flow from the platebattery IOI, thus conserving the life of both the filament and platebatteries when switch I00 or 98 is open.

Radio-frequency signal energy, at the selected carrier frequency, isconveyed from the plate circuit of vacuum tube 86, throughradio-frequency coupling condenser I02, to one side of a crystal diodedetector I03. Resistor I04 is also connected between the input side ofdiode detector I03, as shown. The output side of the diode detector I03is connected to one side of volume-control potentiometer I05, themovable arm of which is applied to'earphones I05 or other suitabletransducer, as shown. The other side of potentiometer I05 is connectedto ground, as indicated. Radiofrequency by-pass condenser I01 isconnected between the output side of crystal diode I03 and ground, asillustrated. In order to provide automatic volume control, a, portion ofthe rectified signal energy is applied through resistor 88, to one sideof loop antenna 85, as shown. Thus, rectified grid bias voltage, thevalue of which is proportional to the's'trength of the received carriersignal, is supplied through the winding of loop 85, to the control gridof vacuum tube 86, without requirement of a vacuum tube rectifier forthe automatic volume control function as is customarily employed inconventional radio receivers. While the illustrative receiver utilizes asingle vacuum tube, it is obvious that more than one vacuum tube may beutilized in the receiver as described above for obtaining a greaterreceiver sensitivity or increased radio output voltage in the earphoneswithout altering the functional arrangement of the crystal diodedetector and associated circuit;

What is claimed as new and desired to be secured by Letters Patent ofthe United States, is:

1. In a system for transmission of electrical signal energy toindividuals within a selected seatmg area, the combination of a signalemitting means disposed adjacent a seating area, said signal emittingmeans being positioned to produc'eimaximum signal intensity withinsaidseating area, having a plurality of chairs therein, a carrier wavetransmitter electrically connected to said signal emitting means, meansfor modula'ting' said carrier wave transmitter by audiofrequency signalenergy corresponding to sounds addressed to occupants of said seatingarea, at least one carrier wave receiver disposed within said seatingarea, said receiver having an antenna structure removably disposed on atleast arsenal one in said seating area, means for positionirig saidantenna structure to effect maximum signal pickup from said signalemitting means, a tuniiig head associated with said antenna structureand being a part thereof, said tuning head having a tuning means, acarrier rectifier, tunmg and volume controls, means for removablymounting said tuning head on said chair with said tuning and volumecontrols in a position accessible to the occupant of said chair, and atransducer connected to said tuning head for use by the occupant of saidchair to permit individual reception of said audio frequency signalenergy.

-2. An inductive-carrier group communications system of restricted-rangetype, comprising in combination a horizontal transmitting loop disposedsubstantially around the periphery of a selected seating area, a carriertransmitter electrically connected with said loop, means for modulatingsaid carrier transmitter by audio frequency signal energy, a pluralityof receiving loop structures disposed in a substantially horizontalposition beneath the seats of chairs within said seating area, each ofsaid chairs having a loop structure provided with means thereon forremovably supporting it in a position of maximum signal pickup withrespect to signal energy emitted by said horizontal transmitting 100p,said loop structure also having means for providing an air-dielectricspacing between said receiving loops and the seats of said chairs tominimize the absorptive effect thereof, an inductive carrier tuning headstructurally associated with each of said receiving loops, said tuninghead including a carrier rectifier, tuning and volume control, saidtuning head also having means for supporting it in position at the sideof the seat of each of said chairs with said controls in a substantiallyupright position, accessible to the occupant of said chair, and atransducer connected to said receiver for individual use by an occupantof said chair.

3. An inductive-carrier group-communications system of restricted-rangetype, comprising in combination a horizontal transmitting loop disposedsubstantially around the periphery of a selected seating area, a carriertransmitter electrically connected with said loop, means for modulatingsaid carrier transmitter by audio frequency signal energy, a pluralityof chairs within said seating area, a receiving loop structure disposedin a substantially horizontal position beneath the seat of at least onechair within said seating area, said loop structure having means thereontor removably supporting it in a position of maximum signal pickup withrespect to signal energy emitted by said horizontal transmitting loop,said loop structure also having means for providing an air-dielectricspacing between said receiving loop and the seat of said chair-tominimize the absorptive efiect thereof,

an inductive carrier tuning head structural associated with saidreceiving loop, said tuning head including a carrier rectifier, tuningand volume control, said tuning head also having means for supporting itin position at the side of the seat of said chair with said controlsaccessible to the occupant of said chair and a transducer connected tosaid receiver for individual use by an occupant of said chair.

4. In an inductive carrier system for transmission of signal energy toindividuals within a selected seating area, the combination of ahoriabout a seating area, having a plurality of ehaii's therein, acarrier transmitter electrically con= nected to said transmitting loop,means for modulating said carrier transmitter by audio-ire quency signalenergy corresponding to sounds addressed to occupants of said seatingarea, a plurality of carrier receivers disposed within said seatingarea, each of said receivers having a loop antenna structure removablydisposed within the leg structure area of each of said chairs, means forpositioning each of said loop antenna structures beneath the seat ofeach of said chairs. and in a substantially horizontal plane, means formaintaining suflicient air-dielectric spacing between the bottom of eachof said chairs and each of said loops to restrict absorption of carriersignal energy by said seat, a tuning head associated with said loopstructure and secured thereto, said tuning head having a tuning means, acarrier rectifier, tuning and volume controls, said tuning head beingdisposable in a position accessible to the occupant of said chair, and atransducer connected to said tuning head for use by the occupant of saidchair to permit individual reception of said audio-frequency signalenergy.

5. In an inductive carrier system for transmission of signal energy toindividuals within a selected seating area, the combination of ahorizontal transmitting loop disposed substantially about a seatingarea, having a plurality of chairs therein, a carrier transmitterelectrically connected to said transmitting loop, means for modulatingsaid carrier transmitter by audio-frequency signal energy correspondingto sounds addressed to occupants of said seating area, a pinrality ofcarrier receivers having a loop antenna structure removably disposedwithin the le structure area of each of said chairs, means forpositioning each of said loop antenna structures beneath the seat ofeach of said chairs, and in a plane substantially parallel to said seat,means for maintaining suficient air-dielectric spacing between thebottom of each 01' said chairs and each of said loops to restrictabsorption of carrier signal energy by each of said seats, a tuning headassociated with each of said loop structures, said tuning head having atuning means, a carrier rectifier, tuning and volume controls, means forremovably mounting each of said tunin heads atthe side of each of saidchairs with said tuning and volume controls in a position accessible tothe occupant of each of said chairs, and a transducer connected to eachof said tuning heads for use by the occupant of each of said chairs topermit individual reception of said audio Irequency signal energy.

6. In an inductive carrier system for transmission of audio frequencysignal energy to individuals within a selected seating area, thecombination of a horizontal transmitting loop disposed substantiallyabout aseating area, a carrier transmitter electrically connected tosaid transmitting loop, means for modulating said carrier transmitter byaudio-frequency signal energy corresponding to sounds addressed tooccupants of said seating area, a plurality of carrier receiversdisposed within said seating area, each of said receivers having a loopantenna structure removably disposed between the legs of each of saidchairs, means for positioning each of said loop antenna structuresbeneath the seat of each of said chairs, means for maintainingsuflicient air-dielectric spacing between the bottom of each of saidchairs and each of said loops zontal transmitting loop disposedsubstantially to restrict absorption of carrier signal energy by 15 siiid soat, a tuning head associated withsaid loop structure, said tuninghead having a tuning meals, a oan'ier rectifier, tuning and volumec'onholr, means-l'oruemdvably mounting said tuning at the side oi saidachairwith said tunin md volume controls in an upwardly-dhposedposition-accessible? tattle-occupant of said chair,

s'adan earphone connected to said tuning head for use by the occupant-ofsaid chair to permit individual reception'ofsaid' audio frequencysignble'nergy'. n 7

7. An inductive-carrier group communications system of: restricted-rangetype, comprising incombination a horizontal transmitting'loopdisposed'substantially around the periphery of a selected seating area,a carrier transmitter electrically connected with said loop, means formodulating said carrier transmitter by audio frequency signal-energy, aplurality of receivingloop structures disposed in a substantiallyhorizontal position: beneath the seats of chairs within said Iea'tingvarea, said loop structures havingmeans thereon for removablysupporting'them in apositinnof: maximum signal pickup with respect tosignal energy emitted by said horizontal transmltting loop, said loopstructure also having means forproviding an air-dielectric spacirfgbetween said" receiving loops and the seats of said a receiver having atuning head structumlly associated with each of said receiving loops,including a carrier rectifier, tuning and volume control, saidtuningrhead having means for supporting it in position at the side ofthe seatof each of said chairs with said controls in a substantiallyupright position, and an earphone connected to said receiver forindividual use by an occupant of said chair.

8.-In a simultaneous translation system of radio-signal distributiontype, a first speaker's mierophone, a carrier-wave transmitter, meansfor modulating said carrier:wave transmitter by W audio'frequency energyfrom said first speakers microphone, a transmitting loop"antenna dls--posed around an auditorium area in which said speaker's microphone islocated, at least, one tz'anslator's' 'microphone for converting aSpoken translation of the speech entering said speakersrmicrophone into;audio frequency signal energy a second carrier wave transmitter, meansfor individually modulating said second transmitter by said audiofrequencysignal energy from said transiators microphone, means forimpressins-carrier wave-energy from said second carrier wave transmitterat a carrier frequency different from that of said first transmitteruponsaid loop antenna; a radio receiver disposed on at leastindividually conveying to the occupant of said chair audio frequencyenergy corresponding to speech impinging on said first speakers'microifhone' or to speech impinging on said translator's microphone.

9. A receiver for induction-radio communicating systems comprising incombination. a multiturn loop antenna, a housing therefor. a tuning headdisposed on one edge of said loop housing, and carried thereby, saidtuning head including a carrier-frequency discriminating means-a carrierwave detector, and a volume control a head-1 phone connected to saidtuning. head and responsive to the signal output thereof, circuit 7means for connecting said detector arid said headphone in series acrossa portion of said multi-turn' loop, and for connecting saidfrequency-discriminating means across the whole of said-loop-to' improvethe selective response'tnereof, and means for positioning said loophousing beneath the seat of a chair with said tuning head'- adjacent theseat thereof and having said frequency discriminating means and saidvolume control upwardly disposed-on said tuning head to facilitate theuse thereof by an occupantof said chair.

10. An induction radio receiver foruse onchairs-"in' seating areasserved by an inductive carrier communications system, comprising incombination a multi-turn loop'antenna, a'pair of non-conducting sheetmembers positioned at either side of said loop antenna and forming'aprotective housing therefor, a tuning head mounted on one crboth of saidsheet members and at one edge thereoffsaid tuning head including a looptuning means and a crystal diode detector, a headphone connected to saidtuning head and responsive to the output thereof, cit cult means forelectrically connectingsaidlooptuning means across all turnsof saidloopan tenna, circuit means for electrically connecting said crystaldiode detector and said headphone f in series across a small porti'on'ofsaid-loop an-' one: chair withinsa-id' auditorium area,said receiverhavinga loop antenna positioned in a plane parallel to that of saidtransmitting loop antenna and mountable'beneath the seat of saidchainstuning head also forming apart or said receiver and being disposedadjacent said loop antenna, means for supporting said tuning headat theside of said chair adjacent the seat thereof, means on said tuning headfor making said receiver selectively responsive to carrier signals fromeither said firstmentiened transmitter or said second mentionedtransmitter as deter= minedby the occupant ofsaid'chair, andatransducerattached to the output of said receiver for tonne and attheground-end thereof, and adjustable supporting means disposed on saidsheet members adaptable for mounting said sheet members beneath the-seatof a chair and forsup' portL g said tuning head at the side of the seatof said chair in an accessible position for the occupantfthereof.

WILLIAM-S. HA'LSTEAD;

REFERENCES crrsu The following referencesare of record'ifi the

